THE NITROGEN CYCLE for highschool student

nitrogen cycle

1. THE NITROGEN CYCLE

2. Learning Objective Describe how nitrogen is cycled within an ecosystem, including the roles of nitrogen-fixing bacteria (e.g. Rhizobium ) and nitrifying bacteria ( Nitrosomonas and Nitrobacter )

3. Keywords Nitrogen Nitrogen fixation Ammonification Nitrification Denitrification Bacteria Process

4. What is a Nitrogen??

5. Nitrogen is in the atmosphere as N 2 The majority ( 78% ) of the Earth’s atmosphere is N 2. All organisms require nitrogen to live and grow N 2 is an inert gas and cannot be used by plants or animals Nitrogen limits plant growth Nitrogen is easily lost from biological systems Nitrogen

6. Forms of Nitrogen Urea  CO(NH 2 ) 2 Ammonia  NH 3 (gaseous) Ammonium  NH 4 Nitrate  NO 3 Nitrite  NO 2 Atmospheric Dinitrogen N 2 Organic N

7. How Can We Use N 2 ? In order for plants and animals to be able to use nitrogen, N 2 gas must first be converted to more a chemically available form such as ammonium (NH 4 + ) or nitrate (NO 3 -). WE CAN’T!

8. Roles of Nitrogen Plants and bacteria use nitrogen in the form of NH 4 + or NO 3 - It serves as an electron acceptor in anaerobic environment Nitrogen is often the most limiting nutrient in soil and water

9. Nitrogen is a key element for : amino acids nucleic acids ( purine , pyrimidine ) cell wall components of bacteria

10. Nitrogen Cycling Processes Nitrogen Fixation – bacteria convert nitrogen gas (N 2 ) to ammonia (NH 3 ) . Ammonification – bacteria and fungi decompose dead plants and animals and release excess NH 3 and ammonium ions (NH 4 + ) . Nitrification – type of chemosynthesis where NH 3 or NH 4 + is converted to nitrite (NO 2 -) ; other bacteria convert NO 2 - to nitrate (NO 3 -) . Denitrification – bacteria convert NO 2 - and NO 3 - to N 2 .

11. Nitrogen Fixation 1) Human Manufacturing Of Synthetic Fertilizers 2) Environmental 3) Nitrogen-fixing Bacteria And Cyanobacteria Means of Nitrogen Fixation :

12. Nitrogen Fixation HUMAN IMPACT Burning fossil fuels, Using synthetic nitrogen fertilizers, Cultivation of legumes all fix nitrogen.

13. Nitrate NO 3 - Atmospheric fixation Out gassing Plant protein Atmospheric Nitrogen Ammonium NH 4 + Soil organic nitrogen The human impact Biological fixation Industrial fixation

14. Industrial N-Fixation The Haber-Bosch Process N 2 + 3H 2  2NH 3 The Haber process uses an iron catalyst High temperatures (500°C) High pressures (250 atmospheres) The energy require comes from burning fossil fuels (coal, gas or oil) Hydrogen is produced from natural gas (methane) or other hydrocarbon

15. The future of industrial nitrogen fixation Food production relies heavily upon synthetic fertilisers made by consuming a lot of fossil energy Food will become more expensive to produce Nitrogen fixing microbes, using an enzyme system, do the same process at standard temperatures and pressures essentially using solar energy

16. Nitrogen Fixation Environmental High-energy Natural Events Which Break The Bond N 2 Examples: Lightning Forest Fires Hot Lava Flows

17. Root uptake Nitrate NO 3 - Plant protein Soil organic nitrogen Nitrogen from the atmosphere Biological fixation Atmospheric fixation Out gassing Atmospheric Nitrogen 4 000 000 000 Gt

18. Atmospheric nitrogen fixation Electrical storms Lightning provides sufficient energy to split the nitrogen atoms of nitrogen gas, Forming oxides of nitrogen NO x and NO 2

19. Atmospheric Pollution This also happens inside the internal combustion engines of cars The exhaust emissions of cars contribute a lot to atmospheric pollution in the form of NO x These compounds form photochemical smogs They are green house gases They dissolve in rain to contribute to acid rain in the form of nitric acid The rain falling on soil and running into rivers They contribute to the eutrophication of water bodies

20. Nitrogen-fixing Bacteria a nd Cyanobacteria These bacteria form symbiotic relationships with host plants The bacteria live in nodules found in the roots of the legume family of plants (e.g. beans, peas, and clover)

21. The nitrogen fixers Cyanobacteria are nitrogen fixers that also fix carbon (these are photosynthetic) Rhizobium bacteria are mutualistic with certain plant species e.g. Legumes They grow in root nodules Azotobacter are bacteria associated with the rooting /soil zone (the rhizosphere ) of plants in grasslands

22. Some are free-living in soil (E.g., Nostoc , Azotobacter ); others live symbiotically with plants (E.g., Frankia , Rhizobium ). These organisms have nitrogenase , an enzyme that uses N 2 as a substrate. N 2 + 8e - + 8H + + 16ATP -> 2NH 3 + H 2 + 16ADP + 16P i NH 3 is immediately converted to NH 4+ . Bacterial enzymes sensitive to O 2 . Symbiotic fixation rate depends on plant stage. Nitrogen Fixing Bacteria and Cyanobacteria

23. In aquatic environments (like fishtanks ) , blue-green algae ( cyanobacteria ) is an important free-living nitrogen fixer. Nitrogen-fixing bacteria and cyanobacteria

24. Biological Nitrogen Fixation Treatments Yield / g Oats Peas No nitrate & sterile soil 0.6 0.8 Nitrate added & sterile soil 12.0 12.9 No nitrate & non-sterile soil 0.7 16.4 Nitrate added & non-sterile soil 11.6 15.3

25. Nitrogen Fixation R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N 2 O N 2

26. The different sources of fixed nitrogen Sources of fixed nitrogen Production / M tonnes a -1 Biological 175 Industrial 50 Internal Combustion 20 Atmospheric 10

27. Mineralization or Ammonification Decomposers: earthworms, termites, slugs, snails, bacteria, and fungi Uses extracellular enzymes  initiate degradation of plant polymers Microorganisms uses: Proteases, lysozymes , nucleases to degrade nitrogen containing molecules

28. Ammonification Process Nitrogen enters the soil through the decomposition of protein in dead organic matter Amino acids + 1 1 / 2 O 2  CO 2 + H 2 O + NH 3 This process liberates a lot of energy which can be used by the saprotrophic microbes

29. Mineralization or Ammonification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N 2 O N 2

30. Nitrification

31. Nitrification (Nitrifying) Bacteria add oxygen to nitrogen in two steps : 1 rst step catalyzed by Nitrosomonas . They oxidise it to nitrite: 2 NH 4 + + 3 O 2  2 NO 2 - +2 H 2 O+ 4 H + 2 nd step catalyzed by Nitrobacter . They oxidise the nitrite to nitrate: 2 NO 2 - + O 2  2 NO 3 -

32. Nitrification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N 2 O N 2

33. Nitrification

34. Denitrificatio n

35. Denitrification R emoves nitrogen from ecosystems, and converts it back to atmospheric N 2. Nitrates and nitrites can be used a source of oxygen for Pseudomonas bacteria 4NO 3 - + C 6 H 12 O 6  2N 2 + 6 H 2

36. Denitrification R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N 2 O N 2

37. Have You Ever Started a Fishtank ? Why must you wait to add a bunch of fish? Like all living creatures, fish give off waste products (pee and poo ). These nitrogenous waste products break down into ammonia (NH 3 ) , which is highly toxic to most fishes.

38. Eutrophication Nutrient enrichment of water bodies Nitrates and ammonia are very soluble in water They are easily washed (leached) from free draining soils These soils tend to be deficient in nitrogen When fertiliser is added to these soils it too will be washed out into water bodies There algae benefit from the extra nitrogen This leads to a serious form of water pollution

39. Fertilisers washed into river or lake New limiting factor imposes itself Decomposers (bacteria) increase in numbers Dead leaves ALGAL BLOOM Rapid growth of algae Death of algae Sewage or other organic waste Eutrophication

40. Increased Biochemical Oxygen Demand (BOD) Hot water from industry (Thermal pollution) Pollution from oil or detergents Decomposers (bacteria) increase in numbers Reduction in dissolved O 2 Making things worse!

41. The death of a lake Death/emigration of freshwater fauna Methaemoglobinaemia in infants Stomach cancer link (WHO limit for nitrates 10mg dm -3 ) Increased nitrite levels NO 3 -  NO 2 - ANAEROBIC CONDITIONS Reduction in dissolved O 2

42. Making things better The need for synthetic fertilisers can be reduced by cultural practices Avoiding the use of soluble fertilisers in sandy (free draining soil) prevents leaching Rotating crops permits the soil to recover from nitrogen hungry crops (e.g. wheat) Adding a nitrogen fixing crop into the rotation cycle Ploughing aerates the soil and reduces denitrification Draining water logged soil also helps reduce denitrification

43. Any Questions???